Testing stuff module - download both files and put in same folder inside the modules folder

testing_stuff.info

name = Testing stuff
description = Just to test stuff
backdrop = 1.x
type = module

testing_stuff.module

<?php

function testing_stuff_menu() {
  $items['test-link'] = array(
    'title' => 'Test link',
    'page callback' => 'testing_stuff_test_link_page',
    'access callback' => TRUE,
    'type' => MENU_CALLBACK,
  );
  return $items;
}

function testing_stuff_test_link_page() {
  $my_link = theme('link', array('text' => 'Link', 'path' => '<front>'));
  return $my_link;
}

function testing_stuff_preprocess_link(&$variables) {
  debug($variables);
}